Thermal processing susceptor

ABSTRACT

In one embodiment, a susceptor for thermal processing is provided. The susceptor includes an outer rim surrounding and coupled to an inner dish, the outer rim having an inner edge and an outer edge. The susceptor further includes one or more structures for reducing a contacting surface area between a substrate and the susceptor when the substrate is supported by the susceptor. At least one of the one or more structures is coupled to the inner dish proximate the inner edge of the outer rim.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/109,945, filed Aug. 23, 2018, which is a divisional of U.S. patentapplication Ser. No. 14/698,793, filed Apr. 28, 2015, which claimsbenefit of U.S. Provisional Patent Application Ser. No. 62/001,562,filed on May 21, 2014, which are each herein incorporated by reference.

FIELD

Embodiments of the present disclosure generally relate to a susceptorfor thermal processing of semiconductor substrates, and moreparticularly to a susceptor having features to improve thermaluniformity across a substrate during processing.

BACKGROUND

Semiconductor substrates are processed for a wide variety ofapplications, including the fabrication of integrated devices andmicrodevices. One method of processing substrates includes depositing amaterial, such as a dielectric material or a conductive metal, on anupper surface of the substrate. Epitaxy is one deposition process thatis used to grow a thin, ultra-pure layer, usually of silicon orgermanium on a surface of a substrate in a processing chamber. Epitaxyprocesses are able to produce such quality layers by maintaining highlyuniform process conditions, such as temperature, pressures, and flowrates, within the processing chambers. Maintaining highly uniformprocess condition in areas around the upper surface of the substrate isnecessary for producing the high-quality layers.

Susceptors are often used in epitaxy processes to support the substrateas well as heat the substrate to a highly uniform temperature.Susceptors often have platter or dish-shaped upper surfaces that areused to support a substrate from below around the edges of the substratewhile leaving a small gap between the remaining lower surface of thesubstrate and the upper surface of the susceptor. Precise control over aheating source, such as a plurality of heating lamps disposed below thesusceptor, allows a susceptor to be heated within very stricttolerances. The heated susceptor can then transfer heat to thesubstrate, primarily by radiation emitted by the susceptor.

Despite the precise control of heating the susceptor in epitaxy,temperature non-uniformities persist across the upper surface of thesubstrate often reducing the quality of the layers deposited on thesubstrate. Undesirable temperature profiles have been observed near theedges of the substrate as well as over areas closer to the center of thesubstrate. Therefore, a need exists for an improved susceptor forsupporting and heating substrates in semiconductor processing.

SUMMARY

In one embodiment, a susceptor for thermal processing is provided. Thesusceptor includes an outer rim surrounding and coupled to an innerdish, the outer rim having an inner edge and an outer edge. Thesusceptor further includes one or more structures for reducing acontacting surface area between a substrate and the susceptor when thesubstrate is supported by the susceptor, wherein at least one of the oneor more structures is coupled to the inner dish proximate the inner edgeof the outer rim.

In another embodiment, a susceptor for a thermal processing chamber isprovided. The susceptor includes an outer rim surrounding and coupled toan inner dish, the outer rim having an inner edge and an outer edge. Thesusceptor further includes one or more elevated structures relative toan upper surface of the inner dish, the one or more elevated structuresto reduce a contacting surface area between the susceptor and asubstrate to be supported by the susceptor, wherein at least one of theelevated structures is coupled to the inner dish at a location proximatethe inner edge of the outer rim.

In another embodiment, a susceptor for a thermal processing chamber isprovided. The susceptor includes an outer rim surrounding and coupled toan inner dish, the outer rim having an inner edge and an outer edge. Thesusceptor further includes six wedges extending radially inward from theinner edge of the outer rim above the inner dish, wherein each wedge isseparated from two other wedges by a gap. The susceptor further includesa quartz insulating separator disposed between each of the wedges. Eachquartz insulating separator contacting two wedges and the inner edge ofthe outer rim. The susceptor further includes three bumps extending froman upper surface of the inner dish. Each bump is located closer thaneach wedge to a center of the inner dish, wherein no bisection of theinner dish comprises all three bumps.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of theembodiments disclosed above can be understood in detail, a moreparticular description, briefly summarized above, may be had byreference to the following embodiments, some of which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments and are therefore not to beconsidered limiting of its scope to exclude other equally effectiveembodiments.

FIG. 1A is a top sectional view of a susceptor, according to oneembodiment.

FIG. 1B is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 1C is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 1D is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 1E is a partial cross sectional view of a susceptor, according tothe embodiment shown in FIG. 1D.

FIG. 2A is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 2B is a partial cross sectional view of a susceptor, according tothe embodiment shown in FIG. 2A.

FIG. 2C is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 3A is a top sectional view of a susceptor, according to anotherembodiment.

FIG. 3B is a partial cross sectional view of a susceptor, according tothe embodiment shown in FIG. 3A.

FIG. 4 is a partial cross sectional view of a susceptor, accordinganother embodiment.

FIG. 5 is a partial cross sectional view of a susceptor, accordinganother embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

The embodiments disclosed generally relate to a susceptor for thermalprocessing of semiconductor substrates. The embodiments disclosed canimprove thermal uniformity across the surface of a substrate duringprocessing by reducing a contacting surface area between the susceptorand the substrate. Reducing the contacting surface area between thesusceptor and the substrate reduces the amount of heat that istransferred from the susceptor to the substrate by conduction duringprocessing. Embodiments of some structures that can reduce thecontacting surface area between the substrate and the susceptor aredescribed below.

FIG. 1A is a top sectional view of a susceptor 120, according to oneembodiment. The susceptor 120 includes an outer rim 110 surrounding andcoupled to an inner dish 102. The inner dish 102 could be concave withthe center of the inner dish being slightly lower than the edges of theinner dish 102. The outer rim 110 includes an inner edge 112 and anouter edge 114. Susceptors, such as susceptor 120, are generally sizedso that the substrate to be processed on the susceptor fits just insidethe outer rim, such as the outer rim 110. The susceptor 120 furtherincludes lift pins 104 to aid in transferring substrates into and out ofa thermal processing chamber (not shown) housing the susceptor 120.

The susceptor 120 further includes six wedges 122 for reducing acontacting surface area between a substrate (not shown) and thesusceptor 120 when the substrate is supported by the susceptor 120,wherein the wedges 122 contact the inner dish 102 proximate the inneredge 112 of the outer rim 110. The wedges 122 may be formed as anintegral part of the susceptor 120, or may be attached to the susceptor,for example by welding. Each wedge 122 extends radially inward from theinner edge 112 of the outer rim 110 and each wedge is separated from twoother wedges by a gap 124. The gaps 124 correspond to areas of theunderside of the substrate that will not contact the susceptor 120allowing for more heat to be radiated from the susceptor 120 to thesubstrate during processing while reducing conductive heating at thesubstrate edge. Each wedge 122 is an elevated structure relative to anupper surface of the inner dish 102. The wedges 122 can be symmetricallyarranged around the center of the inner dish 102. Each wedge 122 couldcontact the inner edge 112 of the outer rim 110 and each wedge 122 couldhave an upper surface higher than the upper surface of the inner dish102. The inner dish, outer rim as well as the wedges could be fabricatedfrom silicon carbide, silicon carbide coated graphite, graphite coatedwith glassy carbon, or other materials with high thermal conductivity.

Although six wedges 122 are shown in FIG. 1A, two or more wedges can beused in different embodiments. FIG. 1B shows a top sectional view of asusceptor 140 with eight wedges 142 separated by gaps 144. FIG. 1C showsa top sectional view of a susceptor 160 with nine wedges 162 separatedby gaps 164. In some embodiments, additional wedges can improve thermaluniformity during processing by reducing the size of the individualsurface areas on the susceptor (i.e., the top surface of each wedge)transferring heat to the substrate by conduction. Additional wedges canimprove thermal uniformity at the edges of the substrate because thereare more gaps where the substrate is not contacting another surface.This improved thermal uniformity helps prevent hotspots from formingalong the edges.

Susceptors 140 and 160 further include three rounded bumps 118 extendingfrom the upper of the inner dish 102. Each bump 118 is located closerthan each wedge 142, 162 to a center of the inner dish 102. The bumps118 could be fastened to inner dish 102 through a threaded connection orother common fastening means. The bumps 118 may be made of the samematerial as the susceptor, or a different material, and may be made fromsilicon carbide, or graphite coated with silicon carbide or glassycarbon. When substrates are supported around the edges, such as when asusceptor is used during processing, the center of the substrate can sagbelow the edges of the substrate. Susceptor dishes, such as the innerdish 102, are often slightly concave to prevent portions of an undersideof a sagging substrate from contacting the susceptor dish duringprocessing. On the other hand, to create the highly uniform processconditions in epitaxy, the distance between the upper surface of theinner dish and the lower surface of the substrate is kept quite low, forexample less than 0.25 mm. If the substrate contacts the dish, heat istransferred from the inner dish to the substrate by conduction andthermal uniformity may be reduced.

The bumps 118 can be used to support a sagging substrate preventingcontact between the inner dish 102 and the substrate. The bumps 118provide a contact surface area between the sagging substrate and thesusceptor that is smaller than the surface area of the substrate thatwould contact the inner dish 102 absent the bumps 118. The bumps 118 canbe evenly distributed around the center of the inner dish 102 as shownin FIGS. 1B and 1C. In some embodiments, to ensure adequate support of asagging substrate there could always be at least one bump 118 on a sideof the inner dish 102.

FIG. 1D is a top sectional view of a susceptor 180, according to anotherembodiment. The susceptor 180 further includes six wedges 182 forreducing a contacting surface area between a substrate (not shown) andthe susceptor 180 when the substrate is supported by the susceptor 180,wherein the wedges 182 contact the inner dish 102 proximate the inneredge 112 of the outer rim 110. Each wedge 182 extends radially inwardfrom the inner edge 112 of the outer rim 110 and each wedge is separatedfrom two other wedges by a gap 184. The gap 184 is larger than the gap124 shown in FIG. 1A to further reduce the contacting surface areabetween the substrate and the susceptor. Susceptor 180 further includesan insulating separator 188 disposed between each of the wedges 182.

FIG. 1E is a partial cross sectional view of the susceptor 180,according to the embodiment shown in FIG. 1D. The cross sectional viewshows the top of the wedge 182 at the same height as the top of theinsulating separator 188. A substrate 50 is shown resting on the top ofthe wedge 182 and the insulating separator 188. The insulating separator188 may be disposed in a groove 189 formed around the susceptor surfacenear the inner edge 112 of the outer rim 110, or at the specified radiallocation of the insulating separator 188. The groove 189 maintains theinsulating separator 188 in a specified location. The insulatingseparator 188 typically has a thickness that is greater than a depth ofthe groove 189 so an upper surface of the insulating separator 188 risesabove the surrounding surface of the susceptor 220, thus reducingcontact between a substrate edge and the susceptor surface.

The insulating separators 188 are typically made from a thermallyinsulating material, such as silicon oxide, quartz of any type (i.e.amorphous, crystalline, optical, bubble, etc.), glass, or the like. Theinsulating separators 188 provide thermal breaks, or areas of reducedthermal conductivity, around the inner dish during processing. Thisthermal break reduces thermal conduction into the edge of the substratefrom the susceptor, which is typically made from a high thermalconductivity material. Reduced contact between the substrate edge andthe highly conductive susceptor material reduces conductive heating ofthe substrate edge during processing. The insulating separators 188 maycontact the inner edge 112 of the outer rim 110, but could also bedisposed at other locations on a susceptor. For example the insulatingseparators 188 may be spaced apart from the inner edge 112 of the outerrim 110.

FIG. 2A is a top sectional view of a susceptor 220, according to anotherembodiment. FIG. 2B is a partial cross sectional view of the susceptor220. Referring to FIGS. 2A and 2B, the susceptor 220 is similar to thesusceptor 120 including an outer rim 210 surrounding an inner dish 202,the outer rim 210 having an inner edge 212 and an outer edge 214. Threelift pins 204 can extend above the inner dish 202.

The susceptor 220 includes concentric annular ridges 222 surrounding thecenter of the inner dish 202. Each annular ridge 222 has a differentdiameter. At least some of the annular ridges 222 can be locatedproximate the inner edge 212 of the outer rim 210. In some embodiments,some of the annular ridges 222 may be located within about 1 mm of theinner edge 212, for example within about 0.5 mm of the inner edge 212.The susceptor 220 may further include six spokes 228 extending from thecenter of the inner dish 202 to the inner edge 212 of the outer rim 210.More or fewer spokes 228 may be included in different embodiments. Eachspoke 228 extends to a different angular location around the inner edge212 of the outer rim 210. In some embodiments, the upper surface of eachspoke 228 is above the tops of the annular ridges 222. In otherembodiments, the upper surface of each spoke could be at substantiallythe same height as the tops of the annular ridges 222. In someembodiments, the annular ridges 222 continue under or through the spokes228 making a complete ring around the center of the inner dish 202. Inother embodiments, the spokes 228 separate portions of the annularridges 222.

The spokes 228 and annular ridges 222 can reduce a contacting surfacearea between a substrate 50 and the susceptor 220 when the substrate 50is supported by the susceptor 220. In some embodiments, the substrate 50may only contact the spokes 228 during processing without contacting theannular ridges 222. In other embodiments, the substrate 50 may contactboth the spokes 228 and at least some of the annular ridges 222 duringprocessing. In some embodiments, the one or both of the annular ridges222 and the spokes 228 or their respective upper surfaces are elevatedstructures relative to the upper surface of the inner dish 202. Theridges 222 may also improve thermal uniformity when processing asubstrate by increasing radiative surface area of the upper surface ofthe susceptor 220.

The spokes 228 and annular ridges 222 may be made of the same materialor a different material, which may be any of the same materials fromwhich the susceptor 220 is made. The spokes 228 and annular ridges 222may be made, in one embodiment, by sculpting the annular ridges 222 froman unpatterned susceptor dish surface. In another embodiment, recessesmay be formed in an unpatterned susceptor dish surface to define thespokes, and then a pattern of ridged pieces attached to the susceptorsurface within the recesses to form the annular ridges 222, for exampleby welding.

In some embodiments, the susceptor 220 can include an angled surface 216connecting the inner dish 202 as well as the spokes 228 and annularridges 222 to the inner edge 212 of the outer rim 210. The angledsurface 216 can be used as part of a supporting surface for thesubstrate 50. Varying the slope or dimensions of the angled surface 216can control the height of the substrate 50 relative to the spokes 228and the annular ridges 222.

FIG. 2C is a top sectional view of a susceptor 240, according to anotherembodiment. Susceptor 220 is similar to susceptor 240 except thatsusceptor 240 does not include any spokes 228. Susceptor 240 includesannular ridges 242 that are similar to annular ridges 222. When asubstrate is placed on susceptor 240, the underside of the substratecould contact at least some of the annular ridges 242 in someembodiments. In other embodiments, there could be a small gap betweenthe underside of the substrate and the tops of the annular ridges 242 asthe substrate is supported by a separate surface, such as angled surface216 of FIG. 2B.

FIG. 3A is a top sectional view of a susceptor 320, according to anotherembodiment. FIG. 3B is a partial cross sectional view of the susceptor320. Referring to FIGS. 3A and 3B, the susceptor 320 is similar to thesusceptor 120 including an outer rim 310 surrounding an inner dish 302,the outer rim 310 having an inner edge 312 and an outer edge 314. Threelift pins 304 can extend above the inner dish 302.

The susceptor 320 includes a series of bumps 322 extending from an uppersurface of the inner dish 302, so at least part of each bump is elevatedabove the inner dish 302. At least some of the bumps 322 can be locatedproximate the inner edge 312 of the outer rim 310. In some embodiments,some of the bumps 322 may be located within about 1 mm of the inner edge312, for example within about 0.5 mm of the inner edge 312. Bumps 322are arranged in a ringed pattern on the inner dish 302, but otherarrangements could be used, such as multiple rings, a triangular,square, or rectangular pattern, or a gridded pattern. In someembodiments, each quadrant of the inner dish 302 could include at leastone bump 322. The bumps 322 could be fastened to inner dish 302 througha threaded connection or other common fastening means.

The bumps 322 can reduce a contacting surface area between a substrate50 and the susceptor 320 when the substrate 50 is supported by thesusceptor 320. In some embodiments, the substrate 50 may only contactthe bumps 322 during processing without contacting the inner dish 302 orany other surface. When the substrate 50 is supported using bumps 322,hot spots around the edges of the substrates are greatly reduced. Inother embodiments, additional bumps, such as bumps 118 shown in FIGS. 1Band 1C could extend up from inner dish 302 at locations closer to thecenter of the inner dish 302 to prevent a sagging substrate fromcontacting the inner dish 302.

The bumps 322 are typically made from a low thermal conductivitymaterial, such as silicon oxide, quartz of any type, glass, etc. Thebumps provide a raised contact for the edge of a substrate disposed onthe susceptor 320 to reduce conductive heating of the substrate edge.The bumps 322 may be inserted into recesses formed in the surface of thesusceptor 320. Features may be added to the bumps 322 and the recessesto allow the bumps 322 to be secured in the susceptor surface. Suchfeatures may include threads or other rotational engagement structures.

FIG. 4 is a partial cross sectional view of a susceptor 420, accordinganother embodiment. The susceptor 420 is similar to the susceptor 120including an outer rim 410 surrounding an inner dish 402, the outer rim410 having an inner edge 412 and an outer edge 414. Three lift pins (notshown) could extend above the inner dish 402.

The susceptor 420 includes an annular ridge 422 extending from an uppersurface of the inner dish 402, so at least part of the annular ridge iselevated above the inner dish 402. The annular ridge can surround thecenter of the inner dish 402 at a a radial distance 424 from the centerof the inner dish 402 that is less than the radius of a substrate 50 tobe supported by the susceptor 420. The annular ridge 422 may be made ofa high thermal conductivity material, such as silicon carbide orgraphite coated with silicon carbide or glassy carbon. A height 426 ofthe annular ridge 422 can be designed to control the gap between thesubstrate 50 and the inner dish 402. In some embodiments, two or moreannular ridges 422 could extend from the upper surface of the inner dish402. The additional annular ridges (not shown) could have differentdiameters as well as different heights from the other annular ridges.Annular ridge 422 is arranged in a ringed pattern on the inner dish 402,but other arrangements could be used, such as multiple rings, atriangular, square, or rectangular pattern, or a gridded pattern. Theannular ridge 422 can be located proximate the inner edge 412 of theouter rim 410. In some embodiments, some of the annular ridges 422 maybe located within about 1 mm of the inner edge 412, for example withinabout 0.5 mm of the inner edge 412.

The annular ridge 422 can reduce a contacting surface area between asubstrate 50 and the susceptor 420 when the substrate 50 is supported bythe susceptor 420. In some embodiments, the substrate 50 may onlycontact the annular ridge 422 during processing without contacting theinner dish 402 or any other surface. The radial location 424 as well asthe height 426 of the annular ridge 422 could be modified to achievedifferent thermal profiles during processing. In other embodiments,bumps, such as bumps 118 shown in FIGS. 1B and 1C could extend frominner dish 402 at locations closer to the center of the inner dish 402to prevent a sagging substrate from contacting the inner dish 402.

FIG. 5 is a partial cross sectional view of a susceptor 520, accordinganother embodiment. The susceptor 520 is similar to the susceptor 120including an outer rim 510 surrounding an inner dish 502, the outer rim510 having an inner edge 512 and an outer edge 514. Three lift pins (notshown) could extend above the inner dish 502.

The susceptor 520 includes an angled surface 522 extending radiallyinward from the inner edge 512 of the outer rim 510 to a depression 526.At least part of angled surface 522 is an elevated structure relative tothe upper surface of the inner dish 502. The upper surface of thedepression 526 is located below the upper surface of the inner dish 502.The upper surface of the depression 526 couples the angled surface 522to the upper surface of the inner dish 502. The angled surface 522 couldbe angled between about three degrees and about twenty degrees from theupper surface of the inner dish 502, such as between about four degreesand about twelve degrees, for example about seven degrees. The angle andlocation of the angled surface 522 can be used to control a radiallocation 524 corresponding to where the substrate 50 can contact theangled surface 522 during processing. The angle and location of theangled surface 522 can also be used to control the size of a gap 528between the bottom of the substrate 50 and the upper surface of thedepression 526. The size of the gap 528 could be between 0.1 mm and 1mm, for example about 0.3 mm.

The angled surface 522 can reduce a contacting surface area between asubstrate 50 and the susceptor 520 when the substrate 50 is supported bythe susceptor 520. In some embodiments, the substrate 50 may onlycontact the angled surface 522 during processing without contacting theinner dish 502 or any other surface. By using a relatively steep angle,such as between about three degrees and about twenty degrees from theupper surface of the inner dish 502, such as between about four degreesand about twelve degrees, for example about seven degrees, a smallersurface area of the substrate edge contacts the susceptor duringprocessing, which reduces the amount of conductive heat that can betransferred from the susceptor 520 to the substrate 50. The angle andlocation of the angled surface 522 could be modified to achievedifferent thermal profiles during processing. In some embodiments,bumps, such as bumps 118, shown in FIGS. 1B and 1C could extend frominner dish 502 at locations closer to the center of the inner dish 502to prevent a sagging substrate from contacting the inner dish 502.

The susceptor embodiments described herein allow for more uniformtemperature control of substrates during thermal processes, such asepitaxy. The temperature control is improved by reducing the surfacearea of the substrate contacting the susceptor, which reduces the amountof conductive heat transferred from the susceptor and the substrate.Conductive heat transfer between the susceptor and the substrate is moredifficult to control than radiant heat transfer, the primary source ofheat transfer between the susceptor and the substrate. Reducing thesurface area of the substrate contacting the susceptor allows for ahigher percentage of the heat transfer to be radiant heat resulting inimproved temperature control and improved depositions on the substrate.The embodiments disclosed reduce the conductive heat transfer near theedge of the substrate by adding a structure, such as a annular ridgearound the center of the inner dish proximate the outer rim, to reducethe contacting surface area between the susceptor and the substrate. Theembodiments disclosed also prevent the possibility of substantialamounts of conductive heat transfer near the center of the substrate byincluding three bumps to support a substrate above the inner dish if thesubstrate sags.

Although the foregoing embodiments have been described using circulargeometries (e.g., inner dish, outer rim, annular ridge, etc.) to be usedon semiconductor “wafers,” the embodiments disclosed can be adapted toconform to different geometries.

While the foregoing is directed to typical embodiments, other andfurther embodiments may be devised without departing from the basicscope thereof, and the scope thereof is determined by the claims thatfollow.

1. A susceptor for a thermal processing chamber comprising: an innerdish; an outer rim surrounding the inner dish, the outer rim having aninner edge and an outer edge; a depression having an upper surfacelocated below an upper surface of the inner dish; and an angled surfaceextending radially inward from the inner edge of the outer rim to thedepression.
 2. The susceptor of claim 1, wherein the upper surface ofthe depression couples the angled surface to the upper surface of theinner dish.
 3. The susceptor of claim 1, wherein the angled surfaceextends from a height below the upper surface of the inner dish to aheight above the upper surface of the inner dish.
 4. The susceptor ofclaim 1, further comprising a series of bumps extending from the uppersurface of the inner dish.
 5. The susceptor of claim 4, wherein eachbump of the series of bumps extends to a top height below a highestheight of the angled surface.
 6. The susceptor of claim 4, wherein theseries of bumps comprises at least three bumps.
 7. The susceptor ofclaim 6, wherein no bisection of the inner dish comprises all threebumps.
 8. The susceptor of claim 1, wherein the angled surface is angledbetween about three degrees and about twenty degrees relative to theupper surface of the inner dish.
 9. The susceptor of claim 1, whereinthe angled surface is angled between about four degrees and about twelvedegrees relative to the upper surface of the inner dish.
 10. A susceptorfor a thermal processing chamber comprising: an inner dish comprising aninner portion having a first upper surface and an outer depressionhaving a second upper surface below the first upper surface; an outerrim surrounding and coupled to the inner dish, the outer rim having aninner edge and an outer edge; and an annular ridge extending from thesecond upper surface of the outer depression of the inner dish andsurrounding a center of the inner dish at a radial distance from thecenter of the inner dish, wherein a height of the annular ridgeincreases and then decreases with increasing distance from the center ofthe inner dish.
 11. The susceptor of claim 10, wherein the annular ridgeis located within 0.5 mm of the inner edge of the outer rim.
 12. Thesusceptor of claim 10, wherein a top height of the annular ridge isbelow an upper surface of the outer rim.
 13. The susceptor of claim 10,wherein the annular ridge comprises silicon carbide.
 14. The susceptorof claim 10, wherein the annular ridge comprises graphite coated withsilicon carbide.
 15. A method of supporting a substrate duringprocessing placing a substrate in a processing position on a susceptorthat is disposed in a process chamber, wherein the susceptor comprises:an inner dish comprising an upper surface; an outer rim surrounding andcoupled to the inner dish, the outer rim having an inner edge and anouter edge; a supporting structure located proximate the inner edge,wherein the supporting structure includes a supporting surface locatedat a height above the upper surface of the inner dish and the substrateis positioned on the supporting surface when the substrate is in theprocessing position; and a plurality of bumps extending from the uppersurface of the inner dish to a top height below the height of thesupporting surface of the supporting structure; and performing a processon the substrate inside the process chamber when the substrate is in theprocessing position on the susceptor.
 16. The method of claim 15,wherein a portion of the substrate contacts at least one of the bumpsduring the processing of the substrate.
 17. The method of claim 15,wherein the supporting structure is located within 1 mm of the inneredge of the outer rim.
 18. The method of claim 15, wherein the pluralityof bumps consists of two or three bumps.
 19. The method of claim 15,wherein the supporting structure is an annular ridge surrounding acenter of the inner dish.
 20. The method of claim 15, wherein thesupporting structure is an angled surface extending radially inward fromthe inner edge of the outer rim towards the inner dish.